Typically, electronic transaction systems, such as vending machines, electronic gaming devices, and other electronic acceptors, include discriminators to determine the authenticity of one or more inserted items of value, for example, coins. Additionally, the discriminators may be used for recognition, to determine the content or denomination of the item of value. Typically, the discriminators measure one or more properties of the items of value, such as dimensions, conductivity, and magnetic permeability, for authentication and/or recognition purposes. Such discriminators may include one or more sensors to measure properties of the coins. Examples of sensors include optical, acoustic, impact and electromagnetic sensors.
Electromagnetic sensors, for example, are operated to induce eddy currents in a coin, and obtain a response of how the magnetic field varies due to the presence of a coin. Responses measured by the electromagnetic sensors can be related to properties of the coin. In another example, the electromagnetic sensor can obtain a response of how the magnetic field varies due to the presence of inks, which are printed on banknotes and are known to exhibit electromagnetic properties.
The responses may be in the form of sensor output signals, which are typically modeled either by time domain or by frequency domain techniques for determining properties of the inserted item of value. The time domain techniques can be very sensitive to variations from unit to unit. Additionally, the time domain techniques are known to be computationally intensive and complex. Time and frequency domain techniques also introduce considerable quantization noise and aliasing in the signals, which may corrupt results of the sensor. One solution for reducing the quantization noise and aliasing is to sample the signal at a sampling rate that is substantially higher than the Nyquist rate. However, this solution comes at the expense of system complexity. Alternatively, the quantization noise can be reduced by band-limiting the signal via filtering. However, additional cost is associated with a high order anti-aliasing filter. Therefore, there exists a need for lower cost and reduced complexity means for determining properties of the inserted item of value.